A surprising study found that there are hints of biological activity on distant planets. Now, scientists say this story has more

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A small sign revealed in April seems likely to change the universe as we know it.

Astronomers detected only one hint, a line of two molecules that rotated in a distant planetary atmosphere called K2-18b, which are molecules on Earth that are produced only by organisms. It's an attractive prospect: the most promising evidence to date shows alien biosignatures, or traces of life associated with biological activities.

But only a few weeks later, new findings suggest that the search must continue.

“It's exciting, but it immediately raised several red flags because the claim for potential biosignatures would be historic, but the importance or intensity of statistical evidence seems to be too high for the data,” said Dr. Luis Welbanks, a postdoctoral research scholar at the School of Earth and Earth Space Exploration at Arizona State University.

Although the molecules identified on K2-18b in April (dimethylsulfide, DMS, disulfide disulfide or DMD) were mainly related to microbial organisms on our planet, scientists noted that these compounds can also form in the absence of life. Now, a team of three non-participants in the study, including Welbanks, have evaluated the models and data used in the original biosignature discovery and achieved very different results, which they have submitted to peer review.

Meanwhile, the lead author of the April study, Nikku Madhusudhan and colleagues conducted other studies, which they said reinforced their previous discoveries about the Earth. Moreover, other observations and studies from multiple groups of scientists are likely to be coming soon.

Successor articles surrounding the research papers around K2-18b provide glimpses of the scientific process unfolding in real time. This is a window into the complexity and nuance of how researchers can find evidence of life outside of Earth, and illustrates why the burden of proof is so high and difficult to reach.

Noisy data

Located 124 light years on Earth, K2-18B is often considered a worthy target for searching for signs of life. According to research led by Madhusudhan, a professor of astrophysics and external sciences at the Institute of Astronomy at the University of Cambridge, it is believed that this is a seawater world, a planet completely covered with liquid water. Therefore, K2-18b quickly attracted attention, a potential habitable place outside our solar system.

Madhusudhan and his Cambridge colleagues’ commitment to K2-18B convinced James Webb’s space telescope’s observation of Earth in operation to further study Earth. But two University of Chicago scientists, Dr. Rafael Luque, a postdoctoral scholar in the university’s department of astronomy and astrophysics, and Michael Zhang, 51 Pegasi B/Burbidge Postdoctoral researcher, found some problems.

Luque said that after reviewing the April paper by Madhusudhan and his team (successfully conducted a 2023 study), Luque and Zhang noticed that the Webb data looked “noisy”.

Noise is caused by imperfections in the telescope and the rate at which different light particles reach the telescope, which is just a challenge for astronomers to study distant exoplanets. Zhang said noise distorts observations and introduces uncertainty into the data.

Trying to detect specific gases in the atmosphere of distant exoplanets introduces more uncertainty. Zhang said the most obvious feature of gases from bonds between hydrogen and carbon molecules is that this connection can stretch, bend and absorb light at different wavelengths, making it difficult to determine the detection of a molecule.

“The problem is basically that every organic molecule has a carbon-hydrogen bond,” Zhang said. “These molecules have hundreds of millions of dollars, so these characteristics are not unique. If you have perfect data, you can distinguish different molecules. But if you don't have perfect data, there are a lot of molecules, especially organic molecules, especially very similar molecules, especially in near aromatics.”

Luque and Zhang further delve into it, and also noted that the perceived temperature of the Earth appears to have risen sharply from the range of about 250 Kelvin to 300 Kelvin (-9.67 F to 80.33 F OR -23.15 C to 26.85 C) in Madhusudhan in 2023 in the 2023 study (29.299.299.99.99.99). study.

Zhang said such harsh temperatures could change the way astronomers think about the potential habitability of the planet, especially because cooler temperatures persist on top of the atmosphere – areas that Weber can detect, while the surface or ocean below may have higher temperatures.

“It's just a deduction from the atmosphere, but it certainly affects how we think of the earth,” Luque said.

Part of the problem, he said, is that the April analysis did not include data collected by the Madhusudhan team in all three Webber instruments over the past few years. Therefore, Luque, Zhang and colleagues conducted a study that combined all available data to see if they could achieve the same results, and even find higher amounts of dimethyl sulfide. They found that there was insufficient evidence for these two molecules in the Earth's atmosphere.

Instead, Luque and Zhang's team discovered other molecules, such as Ethane, could fit the same profile. But ethane does not mean life.

Evidence of disappearance

Well Banks of Arizona State University and colleagues, including Matt Nixon, a postdoctoral fellow in the University of Maryland’s Park Astronomy Department, also found the basic questions they believed to have published their papers in K2-18B in April.

Wellbanks said the concern was in how Madhusudhan and his team created models to show which molecules might be in the atmosphere of the Earth.

“Each (molecule) was tested for the same minimum baseline at a time, which means every model has an artificial advantage: This is the only allowed explanation,” Welbanks said.

When Welbanks and his team conducted their own analysis, they expanded the model from Madhusudhan's research.

“(Madhusudhan and his colleagues) do not allow any other chemical species that may produce these small signals or observations,” Nixon said. “So the main thing we have to do is to evaluate whether other chemical species can provide sufficient fit for the data.”

When the model expanded, evidence for dimethyl sulfide dimethyl or disulfide disulfide disulfide “just disappeared.”

Prosecution

Madhusudhan believes the research conducted after his April paper was “very encouraging” and “a healthy discussion of our interpretation of the K2-18B data.”

He reviewed Luque and Zhang's work and agreed that their findings did not show “strong discovery of DMS or DMD”. When Madhusudhan's team published the paper in April, he said the observations reached a one-third level of significance, or the probability of accidental detection was 0.3%.

For a scientific discovery that is extremely unlikely to happen by chance, the observations must reach five sigma thresholds, or below 0.00006%. Hurry Banks said reaching such a threshold would require many steps, including repeated detection of the same molecule using multiple telescopes and excluding potential non-biological sources.

While this evidence can be found in our lives, it is unlikely to be the Eureka moment, and slower architecture requires consensus among astronomers, physicists, biologists and chemists.

“We have never reached such evidence,” Madhusudhan wrote in an email. “In our previous two studies, we found only or below the evidence of 3-sigma (Madhusudhan et al., 2023 and 2025). We call it a moderate evidence or tip, but not stressed. I agree with (Luque and Zhang's) claims, which is consistent with our study, which we have already conducted strong evidence in our study and have expanded and communicated in our study, and communication. ” and communicate.

In response to the research conducted by the Welbanks team, Madhusudhan and his Cambridge colleagues wrote another manuscript that expanded the search on K2-18B, which included 650 types of molecules. They submitted new analysis for peer review.

“This is by far, using all available data from K2-18B and searching through 650 molecules, the largest search for chemical characteristics in exoplanets to date,” Madhusudhan said. “We found that DMS remains a promising candidate molecule in this planet, although as we pointed out in previous studies, more corporate detection observations are needed.”

Wellbanks said Wellbanks and Nixon were pleased that Madhusudhan and his colleagues talked about the concerns raised, but believed the new paper effectively returned to the central claim put forward in the original April study.

“The new paper acknowledges by default that DMS/DMDS detection is not powerful, but still relies on the same flawed statistical framework and selective reading of its own results,” Welbanks said in an email. “Although the tone is more cautious (sometimes), the approach still masks the true level of uncertainty. The statistical significance claimed in early work is the product of unrecognized arbitrary modeling decisions.”

Luke said Cambridge’s new paper is a step in the right direction as it explores other possible chemical biosignatures.

“But I think it’s inadequate,” Luke said. “I think it’s too restrictive of being a rebuttal of (Welbanks) paper.”

However, astronomers studying K2-18B agree that moving forward in studying exoplanets helps the scientific process.

“I think it's a good, healthy scientific argument to talk about what's going on on this planet,” said Wellbanks. “No matter what any single author says now, we don't have silver bullets. But that's why it's exciting because we know we're the closest we've ever been (find a biosignature), and I think we might get it in our lifetime, but now we're not there, it's not a failure. We're testing bold ideas.”

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